Composite materials are the latest generation of lightweight and extremely strong materials. Currently, most military and commercial aircraft include large amounts of composite materials to achieve a strong, lightweight structure. However, the full potential of composite materials has not yet been realized in many commercial applications.
A typical composite material includes an extremely strong fiber, such as fiber glass, carbon (or graphite) fiber, boron fiber, KEVLAR®, or the like, suspended within a matrix, which is typically made of a polymer resin, such as epoxy. The matrix is typically much weaker structurally than the fiber.
The most common composite materials include short sections of chopped fiber mixed in with a resin. The resin-fiber mixture can be easily sprayed or smeared on a form to create a wide variety of shapes, such as fiberglass boat hulls. Such “engineering composites,” as they are called, offer flexibility and ease of use but fail to capture the full strength of the fiber. The composite is limited by the relative weakness of the resin matrix in which the fiber is suspended.
“Advanced composites” seek to remedy this problem by using continuous fibers wrapped around a form or mandrel. Advanced composites also seek to align the fibers such that their load bearing capacity is improved. Prior apparatus and methods for forming advanced composites are very limited in the shapes that may be made therewith. The principle limitation stems from the fact that prior systems rotate the part relative to a spool of filament. Shapes having closed loops, substantially closed loops, sharp angles, and branches are all impossible to wrap with a continuous filament where the workpiece is rotated. At higher speeds in particular, such shapes are eccentric and prone to vibration. Typically, parts made using prior systems are symmetric about a single axis and substantially straight, such as tubes or cylindrical tanks.
A “centerless wheel” approach has been used in the field of composites for in situ wrapping of roadway support pillars and for other large, straight structural members. In the centerless wheel method, a filament source moves within a circular race, or “centerless wheel,” surrounding the part. Such apparatus typically require that the entire workpiece pass through a permanently closed race around which the filament source moves or to which the filament source is mounted. Accordingly, shapes having closed loops, substantially closed loops, and branches cannot pass through the race. Other apparatus require extensive setup operations to assemble the circular race around the part to be wrapped and therefore are only practicably used for large straight shapes.
In other fields, tape and wire are applied to toroids and other shapes by mounting the tape or wire source to a circular carrier mounted within the circular race. Some of these systems provide a small gap in the carrier which is allignable with a corresponding gap in the race to permit insertion of a part. However, the small size of the gap limits the size of the part that may be processed. Furthermore, such systems have not been used in the field of composites.
In view of the foregoing, what is needed is a winding apparatus for laying continuous strands of composite material on structural members, including branched, closed loop, substantially closed loop, and sharply angled portions. The race should be readily opened and closed. The race when opened should allow insertion of parts occupying substantially all of the area encircled by the centerless race. It would be a further advancement in the art to provide such an apparatus that may be readily opened is and closed during the processing of an individual part to accommodate parts of varying size and structure.